Catalyst and process for the isomerization of olefins in the presence of reactive impurities

ABSTRACT

A process and catalyst for isomerizing olefins are disclosed. The process and catalyst are particularly useful for isomerizing alkenyl bridged ring compounds to the corresponding alkyladiene bridged ring compounds. In one embodiment, the isomerization catalyst comprises an oxygen treated mixture of an alkali metal on a dried support having a surface area of 125 to 195 m 2  /g when the support consists essentially of alumina wherein the alumina precursor is a large crystallite pseudoboehmite. The catalyst is particularly useful for isomerizing 5-vinyl-2-norbornene to 5-ethylidiene-2-norbornene. The catalyst is very active and highly selective and resistant to catalyst poisons. The process contacts the catalyst with an alkenyl bridged ring compound and yields the corresponding alkyladiene bridged ring compound.

This application is a continuation-in-part of application Ser. No.08/405,650, filed on Mar. 17, 1995, now abandoned, which is acontinuation-in-part of application Ser. No. 08/150,946, filed on Nov.12, 1993, now abandoned, which is a continuation-in-part of applicationSer. No. 07/775,776, filed on Oct. 11, 1991, now abandoned, which is acontinuation-in-part of application Ser. No. 07/700,016, filed on May14, 1991, now abandoned, all of which are incorporated by reference intheir entirety herein for purposes of U.S. practice.

FIELD OF THE INVENTION

The present invention relates to a process for isomerizing olefins, andparticularly for isomerizing alkenyl bridged ring compounds to thecorresponding alkylidene bridged ring compound by use of a highly activeand highly selective isomerization catalyst in the presence of reactiveimpurities. The process of the invention may be used to isomerize5-vinyl-2-norbornene (hereinafter "VNB") to 5-ethylidene-2-norbornene(hereinafter "ENB"), which is used commercially in the production ofelastomeric polymers and synthetic rubber. The process of the inventionmay also be used to isomerize a terminal olefin to an internal olefinwhich may be used as a reactant in the synthesis of chemicals or as analkylation feedstock to yield octane enhancing gasoline additives. Thehighly active isomerization catalyst is prepared by adding an alkalimetal to alumina and then activating the mixture by careful oxidation ofthe alkali metal.

DESCRIPTION OF THE PRIOR ART

The isomerization of olefins is well-known. Olefins are often isomerizedto produce the type of olefin necessary for a chemical synthesis or fora process for making fuels or fuel additives. For instance, the use ofENB as a monomer in the production of rubbery polymers is well known.ENB may be produced by reacting 1,3-butadiene and cyclopentadiene in anaddition reaction commonly known as a Diels-Alder reaction, yielding VNBwhich is then catalytically isomerized to ENB.

Known isomerization catalysts include liquid bases, such as mixtures ofalkali metal hydroxides and aprotic organic solvents, mixtures of alkalimetal amides and amines, and mixtures of organic alkali metal compoundsand aliphatic amines. Unfortunately, the catalytic activity of theliquid bases is relatively low, and therefore a large amount of theseexpensive catalysts must be used. Also, recovery of the catalyst fromthe reaction mixture is very difficult, requires complicated separationand recovery steps and consumes a large amount of energy.

Solid isomerization catalysts are also known, for example, alkali metalscarried on large surface area anhydrous supports such as activatedcarbon, silica gel, alumina and the like. These solid catalysts aredifficult to handle because they may ignite and lose activity on contactwith oxygen. Also, the isomerization performance of these solidcatalysts is poor, because conversion and selectivity are low.

U.S. Pat. No. 3,405,196 (Wolff) teaches the use of an alkali metalcatalyst which is primarily used to convert 1-pentene to 2-pentene and1-butene to 2-butene and is not used to isomerize alkenyl bridged ringcompounds. The patent focuses on a process in which a terminal olefin isconverted to an internal olefin in the presence of a supportedalkali-metal catalyst that has been pretreated with an oxygen containinggas such as nitrous oxide. The catalyst used contains an alkali metaldispersed on a high-surface area, substantially inert support. Thealkali metal may be selected from sodium, potassium, rubidium andcesium. The desired catalyst support material is a high surface area,large pore, and slightly acidic alumina.

The patent discloses a preferred temperature between 300° C. and 400° C.for dispersion of sodium on alumina. This would be impractical forcommercial use since most catalyst preparation equipment can notfunction at such high temperatures.

The patent does not disclose the importance of surface area of thesupport and its relationship to resulting catalyst activity. The patentfails to teach or recognize the presence of any impurities in the olefinfeed and does not disclose the importance of catalyst poisons orreactive impurities in the feed stream and its relationship to resultingcatalyst activity.

Reactive impurities are defined to be such impurities in the feed streamwhich do not act as isomerization catalyst poisons, but are highlyreactive and detrimental to use in the downstream process ofpolymerization.

U.S. Pat. No. 4,727,204 (Sumitimo) teaches a 5-vinyl-2-norbornene (VNB)feedstream can handle only up to 0.5 wt. % VCH impurity to make highpurity ENB. When the VNB feedstream contains more than 0.5 wt % VCH, thequality of produced 5-ethylidene-2-norbornene (ENB) is unsatisfactory sothat it cannot be used without additional purification as the thirdmonomer in the production of EPDM. To produce ENB with high quality, itis essential to isomerize VNB containing less than 0.5 wt. % VCH.

The prior art catalysts are either pyrophoric or lack desirably highactivities. These and other disadvantages of the prior art are overcomeby the present invention, which provides a new selective and efficientcatalyst for isomerization of olefins which, in addition, is resistantto catalyst poisons. Also the prior art is either silent on the issue ofcatalyst poisons or teaches that reactive feedstream impurities wouldinhibit the production of high purity ENB.

SUMMARY OF THE INVENTION

The present invention relates to a process and catalyst for isomerizingolefins, and particularly to isomerizing alkenyl bridged ring compoundsto the corresponding alkylidene bridged ring compounds by use of ahighly active and highly selective isomerization catalyst in thepresence of reactive impurities contained in the olefins. In a preferredembodiment, the process of the invention is used for isomerizing animpure stream of 5-vinyl-2-norbornene (VNB) an alkenyl bridged ringcompound, to make high purity quality 5-ethylidene-2-norbornene (ENB),an alkylidene bridged ring compound, which is used commercially as thediene monomer in ethylene-propylene-diene monomer rubber (EPDM).

One embodiment of the invention provides an activated isomerizationcatalyst prepared by:

a) providing a substantially dry support material;

b) mixing a metallic form alkali metal and the dry support materialunder conditions of time and elevated temperature to produce a catalystprecursor mixture comprising a substantially uniform dispersion of thealkali metal on the support;

c) subjecting the catalyst precursor mixture to continued heat treatmentat a temperature of at least 130° C. for a time of at least 30 minutes;and

d) activating the heat treated catalyst precursor mixture by treatmentwith an oxygen-containing gas.

The invention also includes an isomerization process utilizing thisactivated catalyst for olefins. One preferred embodiment includes aprocess for catalytically isomerizing a stream comprising an alkenylbridged ring compound which further comprises one or more reactiveimpurities which comprises contacting the stream comprising an alkenylbridged ring compound which further comprises one or more reactiveimpurities with an activated catalyst, wherein the activated catalyst isprepared by:

a) providing a substantially dry support material wherein saidsubstantially dry support material consists essentially of an aluminahaving a surface area in the range of 140 to 180 m² /g when preparedfrom a starting material consisting of a large crystallitepseudoboehmite or having a surface area in the range of 230 to 260 m² /gwhen prepared from a starting material consisting of a small crystallitepseudoboehmite;

b) mixing a metallic form alkali metal wherein said alkali metal issodium and the dry support material under conditions of time andelevated temperature to produce a catalyst precursor mixture comprisinga substantially uniform dispersion of the alkali metal on the support;

c) subjecting the catalyst precursor mixture to continued heat treatmentat a temperature of at least 130° C. for a time of at least 60 minutes;and

d) activating the heat treated catalyst precursor mixture by treatmentwith an oxygen-containing gas at a temperature of 150° C. to 200° C.

In yet another preferred embodiment, the invention provides for aprocess for catalytically isomerizing a stream comprising a5-vinyl-2-norbornene which further comprises one or more reactiveimpurities which comprises contacting the stream comprising a5-vinyl-2-norbornene which further comprises one or more reactiveimpurities with an activated catalyst, wherein the activated catalyst isprepared by:

a) providing a substantially dry support material wherein saidsubstantially dry support material consists essentially of an aluminahaving a surface area in the range of 140 to 180 m² /g when preparedfrom a starting material consisting of a large crystallitepseudoboehmite or having a surface area in the range of 230 to 260 m² /gwhen prepared from a starting material consisting of a small crystallitepseudoboehmite;

b) mixing a metallic form alkali metal wherein said alkali metal issodium and the dry support material under conditions of time andelevated temperature to produce a catalyst precursor mixture comprisinga substantially uniform dispersion of the alkali metal on the support;

c) subjecting the catalyst precursor mixture to continued heat treatmentat a temperature of at least 130° C. for a time of at least 60 minutes;and

d) activating the heat treated catalyst precursor mixture by treatmentwith an oxygen-containing gas at a temperature of 150° C. to 200° C.

A feature of this invention is the high level of VNB conversion and thehigh selectivity to ENB in the presence of reactive impurities. Anotherfeature of this invention is the stability of the catalyst used toeffect isomerization. An object of the invention is to provide anisomerization catalyst which combines high selectivity and conversionefficiency and yet remains non-pyrophoric on contact with air or water.Accordingly, these and other features of this invention will becomeapparent from the following detailed description, wherein reference ismade to the Figures in the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

Catalyst Preparation

The isomerization catalyst of the invention is comprised of an alkalimetal on a dried support material. The preferred embodiment includesfurther treating the combination with a gas containing oxygen. Thealkali metal may be selected from the group of lithium, sodium,potassium, rubidium, cesium and mixtures thereof. The alkali metalconsists essentially of the metal in its elemental state, for example,if potassium is the alkali metal, it should be added as pure potassiumand not in combination with another element, i.e., potassium hydroxide.Two or more alkali metals may be combined in the same catalyst. Sodiumis the preferred alkali metal. The catalyst may be prepared bydispersing 1-40 wt % alkali metal on a dried support material attemperatures above the melting point of the alkali metal, under anatmosphere of dry, inert gas. The preferred embodiment includes theadditional step of subjecting the alkali metal dispersed on the supportmaterial to oxidation by contact with a gas having an oxygen content of0.1 to 25 mole % at temperatures of 0°-300° C. to both activate andpassivate the catalyst.

Support--Composition

Oxides and/or hydroxides of metals of Groups 1A, 2A, 3A, 4A and 4B ofthe Periodic Table may be used as the support material but the supportmaterial may not be a hydrotalcite compound as described in U.S. Pat.No. 4,675,307. The Periodic Table referred to is the table as reproducedin the CRC Handbook of Chemistry and Physics, 53rd edition. Otherexamples of support materials include carbon, graphite, clays,diatomaceous earths, magnesia, titania, zirconia, calcium oxide,magnesium oxide, sodium oxide and barium oxide. The support may includeone or more of these support materials. Alumina is the preferred supportmaterial and in a most preferred embodiment, the support materialconsists essentially of alumina. Alumina consists of mostly Al₂ O₃ andsmall amounts of Na₂ O, SiO₂ TiO₂, and Fe₂ O₃. The alumina utilized inthe most preferred embodiments is prepared from a small or largecrystalline pseudoboehmite alumina. Gibbsite and Bayerite are notsuitable starting aluminas.

Support--Pore Size

The pore size radius of the support material may range from about 5 to1,000 Angstroms more preferably from 10 to 300 Angstroms and mostpreferably from 10 to 100 Angstroms. The support material used forpreparing the catalyst may be in powder, pelletized, or extruded form.The support material should be dried under a dry atmosphere, and itshould be free of water and entrained oxygen after calcination.

Support--Drying

In the preferred embodiment, the support should be dried of absorbedwater prior to contact with the alkali metal. Drying is effected byheating the support material at temperatures of from 100° C. to 1,000°C., more preferably from about 200° C. to about 800° C. and mostpreferably from about 200° C. to about 400° C. The drying may beconducted at atmospheric pressure or higher, however, reduced pressuresare preferred. Preferably an inert gas is purged through the dryingvessel in order to sweep away any water or oxygen molecules which may bedriven off from the support material by the heat. The drying should lastfor from about 0.1 to 100 hours preferably from about 1 to 20 hours. Inthe drying process, the support is heated at a constant temperaturewhich drives water from the support material whereby no free water isleft, thus producing an essentially dry support material. After drying,the support material should be kept under a dry atmosphere so that waterdoes not become associated with the support material.

As mentioned above, drying at temperatures below 400° C. for less than20 hours does not significantly change the surface area of alumina.However, drying at temperatures above 500° C. may result in a decreasein the alumina surface area.

Support--Surface Area

In fact, high temperature heating is used to reduce the surface area ofstarting aluminas from values above 195 m² /g or above 280 m² /g tovalues within the desired ranges of 125-195 m² /g and 220-280 m² /g,respectively. For example, a large crystallite pseudoboehmite aluminawith a surface area of 240 m² /g may be dried at 600° C. for 1 to 6hours to yield an alumina with a surface area of 170 m² /g.

The material of the support upon which the alkali metal should bedispersed may be any normally solid material which has large pores. Inthe most preferred embodiment, the material is alumina and is not ahydrotalcite compound as described in U.S. Pat. No. 4,675,307. Thesupport material should remain in the solid state at the elevatedtemperatures required during drying and alkali metal dispersion.

The preferred surface area range for alumina is a function of thestarting material. The preferred starting material for the aluminasupport is pseudoboehmite, which may be further differentiated by theircrystalline sizes, being large or small. Alumina supports prepared byheating of gibbsite or Bayerite aluminas can not be used in the presentinvention. Calcination is used to reduce the surface area of thesematerials by methods well known in the art in order to obtain thedesired surface area.

The preferred surface area ranges from 125 to 195 m² /g after heating,when prepared from a large crystalline pseudoboehmite such as a catapalgrade alumina. Preferably, the support material has a surface arearanging from about 130 to 190 m² /g, more preferably from about 140 to180 m² /g, and most preferably from about 150 to 180 m² /g. In fact,some surprisingly active catalysts have been prepared from supportmaterial with a surface area of about 170 m² /g. Catalysts with asurface area of about 180 m² /g are also good.

The preferred surface area ranges from 220 to 280 m² /g after heating,when prepared from a small crystalline pseudoboehmite. Preferably, thesupport material has a surface area ranging from about 230 to 270 m² /g,and more preferably from about 230 to 260 m² /g.

Heating, as described herein, at temperatures below 400° C. does notsignificantly change the surface area of the support. The surface areaof the alumina is measured by the BET (Brunauer, Emmett, Teller) methodof nitrogen adsorption and desorption.

Application of Metal Into Support material

The catalytic combination of alkali metal and support material isprepared by first contacting the dried support material with the alkalimetal under a dry, inert, oxygen free atmosphere thus forming a catalystprecursor mixture. The alkali metal is preferably in the molten stateduring at least a portion of the contact and the contact occurs byphysically blending the dried support material with the alkali metalunder the dry, inert, oxygen free atmosphere. In the most preferredembodiment, the catalyst precursor mixture consists essentially of thealkali metal and the support material.

The alkali metal may be in the solid, liquid or gaseous state wheninitially contacted with the dried support material. Usually, theinitial contact occurs at a temperature above the melting point of themetal, preferably from about 1000° to about 150° C. under an inertatmosphere. Gasses such as nitrogen, argon, helium and krypton willprovide an inert atmosphere. If the alkali metal is in the solid statewhen initially contacted with the support material, the temperature ofthe mixture should be raised enough to melt the alkali metal, and themixture should be stirred for initial dispersion of the alkali metal onthe support material. A preferred method for mixing sodium with aluminais to add molten sodium to a gas fluidized bed of alumina powder at atemperature above the melting point of Na.

The mixing agitation may be discontinued after the alkali metal isroughly dispersed on the support material, however, it is preferable tocontinue mixing until the alkali metal is evenly distributed on thesurface of the dried support material. In the case of a mixture ofsodium on alumina, a visual indication of a blue black or blue grayevenly distributed color over the surface of the alumina indicatesuniform distribution of sodium. If large amounts of materials are to bemixed or slow mixing speeds are used, complete uniform dispersion willtake longer, however, mixing is often complete within about 30 minuteswhen a rotary mixer is used to produce 100 grams of catalyst.

The amount of alkali metal which should be distributed upon the driedsupport material is in the range of from about 1 to about 40 wt % basedupon the total weight of the mixture comprising both alkali metal anddried support material. Preferably the range of alkali metal is fromabout 5 to about 20 wt % and most preferably from about 10 to about 15wt %.

Heat Treat

In a preferred embodiment, after dispersion of metal on the support, theuniform dispersion should be agitated for 1-10 hours, preferably 2hours, at the same temperature or higher to ensure complete thermalmixing. The amount of time required for the heat soak step is a functionof mixing temperature. The higher the temperature, the shorter the heattreat time. The temperature should be in the range of the melting pointof the alkyaline metal to 400° C. preferably in the range of 130° C. to300° C. most preferably in the range of 150° C. to 250° C.

At a mixing temperature of 150° C., 2 hours is most preferred and isequivalent to 200° C. for 1 hour treatment.

Oxidation

After the alkali metal has been dispersed upon the dried supportmaterial and heat soaked to form a catalyst precursor mixture, themixture should be contacted with an activating gas containing oxygen.Since a violent reaction between the alkali metal and oxygen will occurif oxygen is added too quickly, care should be taken to avoid exposingthe mixture to excessive oxygen initially. If the temperature of themixture exceeds about 300° C. during the activation, the rate of oxygencontact with the mixture should be reduced. The rate of oxygen contactmay be reduced by lowering the flow rate of oxygen containing gas or byreducing the concentration of oxygen in the oxygen containing gas. Someinert gas flow should be maintained in order to reduce the temperatureof the catalyst mixture to a safe level. Alternatively, pure oxygen atreduced pressure may be used as the activating gas.

In one embodiment of the invention, the catalyst mixture is contactedwith the activating gas at a temperature within the range of from about0° to about 300° C. preferably about 1000° to 250° C. and mostpreferably about 150° to about 200° C. The catalyst mixture may beagitated while the contact with the activating gas occurs.

The activating gas may comprise a single type of gaseous compoundcontaining oxygen or a mixture of an inert gas with another gascontaining oxygen. The activating gas must be dry, since moisture willhinder the ultimate catalyst performance. Examples of activating gasesinclude nitric oxide, nitrous oxide, sulfur dioxide, dry air, ozone, andmixtures of oxygen with nitrogen, helium, argon, krypton, xenon, orradon. Mixtures of these gases or mixtures may also be used. In apreferred embodiment a mixture of oxygen (O₂) in nitrogen (N₂) may beused as the activating gas. The amount of oxygen in the activating gasshould be from about 0.1 to about 25 mole %. Preferably the amount ofoxygen in the activating gas mixture is from about 2 to about 10 mole %and most preferably about 5 mole %. If pure oxygen (100 mole % O₂) isused as the activating gas, the pressure should be reduced to betweenabout 0.001 and 0.25 atmosphere.

If oxygen is only part of an oxygen containing molecule, such as NO orNO₂, the oxygen content of the gas is calculated by dividing the atomicweight of oxygen in the molecule by the molecular weight of the gas.

The contact between the oxygen containing gas and the mixture may becontinued until all of the alkali metal has been oxidized; however, itis preferable to stop the contact when the total contact oxygen toalkali metal atomic ratio is within the range of from about 0.005 toabout 1.0 moles of oxygen per atom of alkali metal. Preferably the ratiois within the range of from about 0.01 to 0.2, more preferably 0.05 to0.18 and most preferably 0.1 to 0.18 moles of oxygen per atom of alkalimetal. These ranges reflect the total moles of oxygen contacted with thealkali metal. At these ranges most, usually all, of the oxygen contactedwith the alkali metal reacts with the alkali metal. This is apparent inFIG. 2 where contact of more than 0.5 moles of oxygen per atom of sodiumdoes not result in further change in catalyst activity.

Isomerization

The catalyst prepared as described above is then used to isomerizeolefins.

The isomerization of olefins described herein relates to the movement ofthe olefinic double bond from its initial position in the olefinicmolecule. It is often necessary to change the location of the doublebond in order to provide the proper reactant for a desired chemicalsynthesis. For instance, linear alpha olefins such as 1-butene,1-pentene, 1-hexene, 1-heptene, and 1-octane may be isomerized to yieldinternal olefins such as 2-butene, 2-pentene, 2-hexene, 3-hexene,2-heptene, 3-heptene, 2-octene, 3-octene and 4-octene. Additionally,branched alpha olefins such as 2-methyl-1-butene and 3-methyl-1-pentenemay be isomerized to 2-methyl-2-butene and 3-methyl-2-pentene,respectively. Internal olefins and branched internal olefins may also beisomerized according to the invention which may be used to isomerize anyolefin with three or more carbon atoms.

The invention is particularly useful in the production of ENB from VNB.The VNB stream to be isomerized may be 90% or more by volume VNB or theVNB stream may be diluted with a solvent that is inert during theisomerization process. Appropriate solvents include aliphatic compoundssuch as hexane, heptane, octane and isooctane, and aromatic compoundssuch as benzene, toluene, xylene and ethylbenzene.

The catalyst may be used to isomerize alkenyl bridged ring compounds,such as VNB, to alkylidene bridged ring compounds, such as ENB. Alkenylbridged ring compounds are of the general formula (I): ##STR1## whereinR¹,R² and R³ are each hydrogen or alkyl having 1 to 8 carbon atoms, R⁴is hydrogen or alkyl having 1 to 4 carbon atoms, and n is 1 or 2 andwherein a double bond may be present at the place between the 2- and3-positions as indicated by the dotted line.

Specific examples of some alkenyl bridged ring compounds are:

5-vinylbicyclo 2,2,1!heptane;

5-(1'-propenyl)-bicyclo 2,2,1!heptane;

5-(1'-butenyl)-bicyclo 2,2,1!heptane;

5-isopropenylbicyclo 2,2,1!heptane;

5-(2'-methyl-1'-propenyl)bicyclo 2,2,1!heptane;

6-methyl-5-vinylbicyclo 2,2,1!heptane;

6-methyl-5-isopropenyl bicyclo 2,2,1!heptane;

6-ethyl-5-vinylbicyclo 2,2,1!heptane;

5-vinylbicyclo 2,2,1!hepta-2-ene;

5-(1'-propenyl)-bicyclo 2,2,1!hepta-2-ene;

5-(1'-butenyl)-bicyclo 2,2,1!hepta-2-ene;

5-isopropenylbicyclo 2,2,1!hepta-2-ene;

5-(2'-methyl-1-propenyl)-bicyclo 2,2,1!hepta-2-ene;

5-(1'-octenyl)-bicyclo 2,2,1!hepta-2-ene;

6-methyl-5-vinylbicyclo 2,2,1!hepta-2-ene;

6-methyl-5-isopropenylbicyclo 2,2,1!hepta-2-ene;

6-ethyl-5-vinylbicyclo 2,2,1!hepta-2-ene;

5-vinylbicyclo 2,2,1!octane;

5-(1'-propenyl)-bicyclo 2,2,2!octane;

5-isopropenylbicyclo 2,2,2!octane;

5-(1'-butenyl)-bicyclo 2,2,2!octane;

6-methyl-5-vinylbicyclo 2,2,2!octane;

6-methyl-5-isopropenylbicyclo 2,2,2!octane;

5-vinylbicyclo 2,2,2!octane;

5-(1'-propenyl)-bicyclo 2,2,2!octa-2-ene;

5-isopropenylbicyclo 2,2,2!octa-2-ene;

5-(1'-butenyl)-bicyclo 2,2,2!octa-2-ene;

5-(2'-methyl-1'-propenyl)-bicyclo 2,2,2!octa-2-ene;

6-methyl-5-vinylbicyclo 2,2,2!octa-2-ene; and

6-methyl-5-isopropenylbicyclo 2,2,2!octa-2-ene.

The compounds represented by formula I can be produced by subjecting acyclic diene such as cyclopentadiene or cyclohexadiene and an aliphatic1,3-diene to a Diels-Alder reaction or by subjecting the correspondingbridged ring compound bearing a hydroxyl group at the 1'- or 2'-position to dehydration.

Isomerization of an alkenyl bridged ring compound shifts the double bondfrom 1'-2' position to the 5-1' position of formula I thereby formingthe alkylidene bridged ring compound. The isomerization is effected bycontacting an alkenyl bridged ring compound, for example, a VNB stream,with the catalyst at temperatures of from about -50° C. to about 200° C.Preferred temperatures of isomerization range from about 0° to about150° C., most preferably from about 20° C. to about 100° C.; however, toachieve high equilibrium conversion, the final reaction temperatureshould be less than 30° C.

Although alkenyl bridges ring compounds can be obtained essentially pureby distillation, it is convenient economically to purify these compoundsto a lessor degree. However, many of the remaining impurities arereactive to strong base catalysts and can act as a catalyst poison.Surprisingly, the sodium on alumina catalysts show good poisoningresistance at low isomerization temperatures.

Such reactive impurities include mono olefins, acidic oxygenates, anddiene impurities, which include the following:

cyclopentadiene (CPD)

cyclooctadiene (COD)

tetrahydroindene (THI)

vinylnorbornadiene (VNBD)

ethynylnorborene (EYNB)

hydroperoxides

vinylcyclohexenes (VCH)

methyl vinylcyclohexenes (MVCH)

The prior art teaches only that CPD has a poisoning effect on thecatalyst which results in the loss of catalyst. The other dieneimpurities are not mentioned in the prior art of isomerization ofalkenyl bridged ring compounds. Moreover, these impurities will havedeleterious effect on ENB used to make EPDM rubber. In contrast, thecatalyst of the invention can perform in the presence of all of theseimpurities to give ENB which is acceptable for use in downstreampolymerization manufacturing processes.

CPD is strongly adsorbed onto the isomerization catalyst and istherefore removed and not included in the isomerization product to givea higher purity product. The CPD levels in the olefin feed stream may befrom 1-1000 wppm of the impurity, preferably from 5 to 500 wppm, andmost preferably from 10-50 wppm.

COD is isomerized by the isomerization catalyst to the 1,3 isomer whichis unreactive and not detrimental to use in the downstreampolymerization process. This effectively gives a higher qualityisomerization product. The catalyst can perform in the presence of from1-10,000 wppm of the COD impurity, preferably from 5 to 1000 wppm, andmost preferably from 10-500 wppm.

THI dehydrogenates with the isomerization catalyst to indan and indene.The indan is isomerized to a non-reactive impurity and the indene isadsorbed and thereby removed from the product stream to give a higherpurity product. The catalyst of the invention can perform in thepresence of from 1-5000 wppm of THI impurity, preferably from 5 to 1000wppm, and most preferably from 10 to 100 wppm.

Both VNBD and EYNB are adsorbed into the isomerization catalyst andthereby removed by from the isomerization product stream to give ahigher purity product. The catalyst can perform in the presence of from1-2000 wppm of each of the VNBD and EYNB impurities, preferably from 5to 1000 wppm, and most preferably from 10 to 500 wppm.

The hydroperoxides are adsorbed by the catalyst and therefore, areremoved and are not present in the product stream to give a higherpurity product. The catalyst of the invention can perform in thepresence of from 1-500 wppm of this impurity, preferably from 5 to 100wppm, and most preferably from 10-50 wppm.

VCH and MCVH dehydrogenate to give aromatic compounds which areunreactive and not detrimental to use in down-stream polymerizationprocess. This effectively gives a higher quality isomerization product.

The catalyst can also perform in the presence of quantities of up to 90wt. % being vinylcyclohexene (VCH) and/or methyl vinylcyclohexene(MVCH), preferably from 0.5 to 90 wt % VCH, more preferably from 0.5 to50 wt. % VCH, and most preferably from 0.5 to 30 wt. % VCH. The levelsof these two typical impurities have been found to not effect thecatalyst performance.

The amount of catalyst used is primarily determined by poison levels,although the use of more catalyst will reduce the time necessary tobring about a given level of conversion at the same temperature.Generally, the weight of alkali metal utilized per weight of alkenylbridged ring compound ranges from 1 part alkali metal per 10,000 partsof alkenyl bridged ring compound to 1 part alkali metal per 500 parts ofalkenyl bridged ring compound. In fixed bed processes, the weightaverage space velocity expressed in terms of weight of feed per hourdivided by the weight of the supported catalyst in the fixed bed shouldrange between 0.1 to 500 Hr⁻¹.

The isomerization process may be conducted at any pressure, however,pressures of from about 0 to about 100 psig are preferred. The reactionmay be conducted in liquid phase or gas phase. A preferred method forconducting the isomerization is to mix a powdered catalyst in a streamof liquid olefin wherein the solid catalyst is suspended in the liquid,such as by stirring. Such a method is disclosed in U.S. Pat. No.5,292,985 entitled "Method of Preparing Isomerization Catalyst", whichis hereby incorporated by reference. Reaction time varies depending onthe reaction temperature, and the amount of catalyst used, but generallyranges from 5 minutes to 6 hours. The isomerization reaction isgenerally conducted in the absence of oxygen and water.

Use of the above described catalyst of the invention in theisomerization of VNB to ENB usually results in nearly completeconversion to ENB and therefore no product purification is necessary.The resulting ENB may be transferred directly to a polymerizationprocess to make EPDM rubber. If for some reason the conversion rates arelower, the ENB may be purified of VNB by distillation.

Although the isomerization of VNB to ENB has been described in moredetail, the catalyst is also useful in the isomerization of olefins ingeneral in the same way as described in reference to VNB isomerization.Conversion percentages herein are determined by subtracting the weightamount of compound remaining after isomerization from the beginningamount of the compound and dividing the result by the beginning amountof the compound. The resulting quotient is multiplied by 100% to expressthe term in percent. Selectivity is determined by dividing the amount ofmaterial converted into desired product by the total amount of materialconverted and multiplying the result by 100% to express the term inpercent.

Particular aspects of the invention may be further understood byreference to the examples below. While these examples are provided tofully illustrate and describe specific features of the invention, theyshould not be construed as limitations on the scope of the invention,which is fully described above.

EXAMPLE I Invention and Comparatives

Alumina powder (30 g) previously dried for 1 hour at 400° C. was placedin a round bottom flask under a nitrogen blanket at room temperaturealong with 4.5 g sodium metal which had been cut into small pieces. Themixture inside the round bottom flask was stirred and heated to 150° C.for 60 minutes. The sodium metal dispersed onto the alumina resulting ina blue-gray powder.

That mixture was then heated to a temperature of 410° C. and stirringwas continued for 60 minutes for heat treat step under a nitrogenatmosphere. Thus the mixing and the heat treat steps were conducted attwo different temperatures. The sodium/alumina mixture was cooled toroom temperature after which, a gaseous stream of 5% O₂ in N₂ was passedthrough the flask at a rate of 126 ml/min until the molar ratio of O₂ tothe initial amount of Na was 0.2:1.

Pure VNB was contacted with 1 or 2 wt % of the catalyst prepared asnoted above. The VNB/catalyst solution was stirred at room temperaturefor 1 hour. A sample of the resulting solution was taken and theconversion of VNB was measured. The activity rate constant wascalculated according to the following formula: In(VNB^(i) /VNB^(f))!÷(catalyst wt % Na)(reaction time in hours)!, where VNB^(i) is theinitial concentration of VNB, and VNB^(f) is the concentration of VNB atthe designated reaction time. The figure clearly shows that when aluminasupport material is prepared by heating a large crystallitepseudoboehmite to give a surface area within the range of 125-195 m² /g,the activity of the catalyst for this reaction can be significantlyimproved over activities of catalysts outside of the desired surfacearea range. More preferably, the surface area of the alumina should bebetween 130 and 190 m² /g, 140 to 180 m² /g and most preferably 150 to180 m² /g. The most active catalyst is prepared from alumina with asurface area of about 170 m² /g.

                  TABLE 1                                                         ______________________________________                                                                          Sur-                                        Exp                     Example   face Catalyst                               No.  Alumina Precursor Material                                                                       Type      Area Activity                               ______________________________________                                         1   Large Crystallite Pseudoboehmite                                                                 Comparative                                                                              6    1                                      2   Gibbsite           Comparative                                                                              85  47                                      3   Gibbsite           Comparative                                                                             100  29                                      4   Gibbsite           Comparative                                                                             115  23                                      5   Gibbsite           Comparative                                                                             126   9                                      6   Gibbsite           Comparative                                                                             127  14                                      7   Gibbsite           Comparative                                                                             136  52                                      8   Large Crystallite Pseudoboehmite                                                                 Invention 141  46                                      9   Large Crystallite Pseudoboehmite                                                                 Invention 163  150                                    10   Large Crystallite Pseudoboehmite                                                                 Invention 156  165                                    11   Large Crystallite Pseudoboehmite                                                                 Invention 167  199                                    12   Large Crystallite Pseudoboehmite                                                                 Invention 172  158                                    13   Large Crystallite Pseudoboehmite                                                                 Invention 178  87                                     14   Large Crystallite Pseudoboehmite                                                                 Comparative                                                                             201  31                                     15   Gibbsite           Comparative                                                                             220  14                                     16   Large Crystallite Pseudoboehmite                                                                 Comparative                                                                             230  25                                     17   Large Crystallite Pseudoboehmite                                                                 Comparative                                                                             130  37                                     18   Large Crystallite Pseudoboehmite                                                                 Invention 141  46                                     19   Large Crystallite Pseudoboehmite                                                                 Invention 164  262                                    ______________________________________                                    

EXAMPLE II Comparative

This example shows the preparation of a catalyst prepared from analumina with a surface area outside of the preferred range and with alower heat treat temperature. Alumina powder (30 g) prepared by heatinga large crystallite pseudoboehmite to give a surface area of 200 m² /gand 4.5 g sodium metal, cut into pieces, or placed into a round bottomflask under a nitrogen atmosphere at room temperature. The mixture wasstirred and heated to 150° C. for 30 minutes. During this step, thesodium metal was dispersed onto the alumina resulting in a bluish-graypowder. The stirring was continued while the temperature was maintainedat 150° C. for 60 minutes. The mixture was then cooled to roomtemperature. A gaseous stream of nitrogen containing 5 mole % oxygen waspassed through the round bottom flask at a rate of 126 ml/min until themolar ratio of O₂ to initial sodium was 0.2:1. The activity rateconstant for this catalyst for isomerization of VNB to ENB at roomtemperature was measured as 15. The test was repeated except that theheat treat temperature was 300° C.

Comparison of these two results show that the temperature of mixingsodium and alumina leads to different catalytic activity even forcatalysts with surface areas outside of the ranges preferred in theinvention.

                  TABLE 2                                                         ______________________________________                                                    Heat Treat                                                        Example     Temperatures °C.                                                                   Catalyst Activity                                     ______________________________________                                        First       300         31                                                    Second      150         15                                                    ______________________________________                                    

EXAMPLE III Invention and Comparative

This example shows the preferred amounts of O₂ added to a catalystduring catalyst preparation.

In each of four separate preparations of catalysts, 30 g alumina powderwith a surface area of 178 m² /g, prepared by heating a largecrystallite pseudoboehmite and 4.5 g sodium metal, cut into pieces, wereplaced in a round bottom flask under a nitrogen atmosphere at roomtemperature. The mixture was stirred and heated to a temperature of 150°C. for 30 minutes. After 30 minutes, the sodium metal was dispersed ontothe alumina and the powder had changed in color to bluish-gray. Thetemperature of the mixture was then raised to 300° C. for 60 minuteswhile stirring continued. The mixture was then cooled to roomtemperature. A nitrogen stream containing 5 vol. % oxygen was thenpassed through the flask at 126 ml/min until the ratio of O₂ to initialsodium was 0.1:1. The catalyst preparation was repeated except that thenitrogen stream containing 5 vol. % O₂ was passed through the flaskuntil the ratio of O₂ to initial sodium was 0.2:1. A third catalyst wasprepared in a similar manner so that the ratio of O₂ to initial sodiumwas 0.5:1. A fourth catalyst was prepared in the same manner except thatno oxygen was added to the mixture of sodium dispersed on alumina. Theresults of an analytical test to determine the amount of unreactedsodium on the catalyst is set forth below in Table 2.

                  TABLE 3                                                         ______________________________________                                                 O.sub.2 /Na                                                                             Example   % Unreacted                                                                             Catalyst                               Example  Ratio     Type      Na Metal  Activity                               ______________________________________                                        First    0.1/1     Invention 33        340                                    Second   0.2/1     Comparative                                                                             5         5                                      Third    0.5/1     Comparative                                                                             5         5                                      Fourth     0/1     Comparative                                                                             81        40                                     ______________________________________                                    

The isomerization activity of the four catalyst prepared above wasmeasured.

As demonstrated in Examples I, II, and III, the catalyst prepared withalumina prepared from a large crystallite pseudoboehmite to have asurface area of about 180 m² /g performed better than those catalystshaving aluminas with surface areas of either 155 or 210 m² /g. Aluminaswith surface areas of about 170 m² /g are most preferred.

EXAMPLE IV

These examples illustrate the effect of varying parameters of oxidation,heat treat temperatures and time and the isomerization of other olefins,in addition to VNB.

Example 4.1

A first catalyst, Catalyst A, was prepared by starting with 30 g aluminapowder (particle size 20-200 micron), surface area of 178 m² /g,prepared by heating a large crystallite pseudoboehmite, was dried at400° C. for 1 hour. It was then placed in a round bottom flask undernitrogen at room temperature along with sodium metal pieces (4.5 g). Themixture was stirred and heated to 150° C. internal temperature for 30min. During this step, the sodium metal dispersed onto the alumina togive a bluish or gray powder. The mixture was then heated in a soakingstep to an internal temperature of 300° C., and stirred for 60 min.except the mixture was oxidized by passing 5% O₂ in N₂ through the flaskat 126 ml/min with stirring until the ratio of O₂ to starting Na was0.2:1. The amount of O₂ added was the stoichiometric amount needed toconvert all the unreacted sodium to Na₂ O. Temperature during theoxidation was 50°-70° C. Analysis of this catalyst showed that 5% of thestarting sodium metal remained unreacted (due to the oxidation).

The catalyst was tested for isomerization activity of5-vinyl-2-norbornene to 5-ethylidene-2-norbornene. The procedure was toadd 5-vinyl-2-norbornene (25 g) to catalyst (0.25 g) with stirring atroom temperature under N₂. After one hour, a sample was withdrawn andanalyzed by gas chromatography. An activity number was calculated asIn(C_(O) /C)!×10², where C_(O) and C are respectively the initial andfinal concentrations of 5-vinyl-2-norbornene.

The catalyst preparation method for Catalyst A was repeated except forvarying the starting surface areas resulting in Examples B, C, D, E, F.The catalysts were then tested for unreacted Na and isomerizationactivity by the procedure given in Example 1. The results are tabulatedbelow in Table 4.1.

                  TABLE 4.1                                                       ______________________________________                                        Catalyst                                                                              Example    Alumina    Na Unreacted                                                                           Activity                               Example Type       Surface Area                                                                             %        Number                                 ______________________________________                                        A       Invention  175         5       120                                    B       Comparative                                                                              200         6       30                                     C       Invention  167        19       250                                    D       Invention  140        25       50                                     E       Invention  126        52       40                                     F       Comparative                                                                              115        --*      20                                     ______________________________________                                         *Not measured                                                            

The results shown in Table 4.1 demonstrate a preferred range of surfaceareas from 125 to 195 m² /g for the alumina support material that givesa catalyst with a higher isomerization activity than those with asurface area outside this range. A more preferred range is 140-180 m² /gand a most preferred range is 150-170 m² /g.

Example 4.2

The catalysts were then tested for isomerization activity other than VNBto ENB.

Catalysts prepared in Examples B-E were tested for activity to isomerize3-methyl-1-pentene, 2-methyl-1-butene, 4-methyl-1-pentene, and1-pentene. The procedure was to add olefin (30 ml) to catalyst (0.25 g)under nitrogen at 0° C. with stirring. After one hour a liquid samplewas removed and analyzed by gas chromatography. An activity number wascalculated in Example 1 except C_(O) and C are respectively the initialand final concentrations of olefin.

The results shown in Table 4.2 below again demonstrate that catalystactivity is greatest when the starting alumina when prepared by heatinga large crystallite pseudoboehmite has a surface area below 200 m² /g.Although there was some effect of olefin structure on isomerizationactivity, the most generally high activity catalyst was prepared fromalumina which had a surface area in the most preferred range found for5-vinyl-norbornene isomerization.

                  TABLE 4.2                                                       ______________________________________                                        Cata-         Alu-    Activity Number                                         lyst  Ex-     mina    3-Methyl-     4-Methyl-                                 Ex-   ample   Surface 1-     2-Methyl-                                                                            1-     1-                                 ample Type    Area    Pentene                                                                              1-Butene                                                                             Pentene                                                                              Pentene                            ______________________________________                                        B     Com-    200      1      1      1      1                                       parative                                                                C     Inven-  167     520    160    55      80                                      tion                                                                    D     Inven-  140     120    240    15     200                                      tion                                                                    E     Inven-  126      70     50    12     180                                      tion                                                                    ______________________________________                                    

Example 4.3

Three tests were run to quantify the effect of heat treat temperatures.Catalysts G, H, and I were prepared by the same procedure as Catalyst A,except with different soak temperatures. The activity of the catalystsprepared were tested for isomerization of VNB by the same procedure usedin Example 4.1.

                  TABLE 4.3                                                       ______________________________________                                                               Heat Treat                                             Catalyst   Example     Temperature                                                                             Activity                                     Example    Type        (°C.)                                                                            Number                                       ______________________________________                                        G          Invention   150       200                                          H          Invention   200       260                                          I          Invention   240       230                                          A          Comparative 300       120                                          ______________________________________                                    

The results shown in Table 4.3 demonstrate that catalyst activity ishighest when the soak temperature is about 200° C.

Example 4.5

Tests were run to get a comparison on the oxidation level and soaktemperature. Catalysts G, J, and K were prepared by the same method asCatalyst A, except with different soak temperatures and oxidationlevels. The activity of the catalysts was tested.

                  TABLE 4.5                                                       ______________________________________                                        Catalyst                                                                             Example  O.sub.2 /Na                                                                            Heat Treat                                                                            Na      Activity                             Example                                                                              Type     Ratio    Temperature                                                                           Unreacted %                                                                           Number                               ______________________________________                                        K      Invention                                                                              0.2/1    150° F.                                                                        11      200                                  L      Invention                                                                              0.1/1    150° F.                                                                        50      100                                  A      Invention                                                                              0.2/1    300° F.                                                                         5      120                                  c      Invention                                                                              0.1/1    300° F.                                                                        33      340                                  ______________________________________                                    

The results in Table 4.5 demonstrate that catalyst activity is highestwhen soak temperature is 300° F. and oxidation level of 0.1/1.

Example 4.6

A safer catalyst can be made when alumina (30 g) with a surface area of167 m² /g was dried for one hour at 400° C. and cooled under vacuum.This alumina was then mixed under N₂ with sodium metal pieces at 150° C.The mixture was oxidized with 5% O₂ in N₂ at 60°-80° C. until the ratioof O₂ /Na was 0.1/1. This procedure was repeated except the time of thesoak step was lengthened to 120 min.

The catalysts were then tested for isomerization activity, the resultsare tabulated below:

                  TABLE 4.6                                                       ______________________________________                                        Catalyst                                                                              Example   Soak      Na Unreacted                                                                            Activity                                Example Type      Time      %         Number                                  ______________________________________                                        6a      Invention  60 min.  50        30                                      6b      Invention 120 min.  50        410                                     ______________________________________                                    

These results show that by lengthening the time of the soak step at 150°C., a higher activity catalyst is obtained.

Example 4.7

It would be best from a catalyst manufacturing perspective, if thecatalyst preparation could be carried out all at 150° C., including theoxidation step. The oxidation step of the catalyst preparation isexothermic by 430 Btu/Lb. and would probably be the most time consumingstep in large scale preparations. To augment heat removal rate, it wouldbe best to run oxidation at as high a temperature as possible. Giventhis 150° C. temperature constraint, two additional examples were run.

Alumina (30 g) with a surface area of 178 m² /g prepared by heating alarge crystallite pseudoboehmite was dried for one hour at 400° C. andcooled under vacuum. This alumina was then mixed under N₂ with sodiummetal pieces at 150° C. for 30 min, and then mixed in a soak step at thesame temperature for 120 min. The mixture was then oxidized with 5% O₂in N₂ while maintaining internal temperature between 150° and 180° C.until the ratio of O₂ /Na was 0.15/1. Analysis showed 10% of thestarting sodium remained unreactive. This catalyst was tested foractivity to isomerize 5-vinyl-2-norbornene with the procedure of Example1.

This same catalyst preparation procedure was repeated, but with analumina starting material that had a surface area of 167 m² /g.

                  TABLE 4.7                                                       ______________________________________                                        Catalyst                                                                             Example   Surface Area,                                                                             Na       Activity                                Example                                                                              Type      m.sup.2 /g  Unreacted %                                                                            Number                                  ______________________________________                                        7a     Invention 178         10       520                                     7b     Invention 162         --       550                                     ______________________________________                                    

An activity number of 550 is the highest activity number possible withthis procedure, and represents the equilibrium conversion of5-vinyl-2-norbornene to 5-ethylidene-2-norbornene.

EXAMPLE V Effect of Reactive Impurities

These examples show the effect of reactive impurities in theisomerization of VNB to ENB, as well as the effect of starting materialof the alumina. The catalysts are prepared using various conditions.

    ______________________________________                                        Catalyst Example                                                                            Description Sub Title                                           ______________________________________                                        A             Comparative -- No oxidation -- Stir --                                        Metallic                                                        B             Invention -- Oxidation -- Molten --                                           Agitation                                                       C             Invention -- Oxidation -- Stir Metallic                         D             Comparative -- Outside Range --                                               No Oxygen                                                       E             Comparative -- Outside Range --                                               Oxidation                                                       F             Comparative -- Outside Range --                                               Oxidation                                                       G             Invention -- Inside Range -- Starting                                         Material                                                        H             Comparative -- Outside Range --                                               Starting Material                                               I             Comparative -- Outside Range --                                               Starting Material                                               ______________________________________                                    

EXAMPLE A Comparative--No oxidation--Stir--Metallic

This example describes one method of catalyst preparation. First,alumina (30 g), prepared by heating a large crystallite pseudoboehmiteto give a surface area of 167 m² /g and a 1.2 wt % loss on ignition at1150° C. is dried in a nitrogen flow at 400° C. for 1 hour and thencooled to room temperature under nitrogen. Then, small pieces ofmetallic sodium (4.5 g) and alumina are placed in a 300 ml round bottomflask equipped with a mechanically driven stir paddle. The mixture isheated under nitrogen to 150° C., and at the point metallic sodiumstarts to melt, stirring is started. The mixture is stirred for 2.5hours, and then cooled to room temperature.

EXAMPLE B Invention--Oxidation--Molten--Agitation

This example describes another method of catalyst preparation. First,alumina (80 lbs), prepared by heating a large crystallite pseudoboehmiteto give a surface area of 172 m² /g and a 1.2 wt % loss on ignition at11 50° C. is dried at 350° C. for 1 hour in a nitrogen flow. The aluminais cooled to 150° C., and molten sodium (12 lb) is added at 6 lb/hrunder nitrogen with agitation. The mixture is stirred 2 hours, and thena mixture of 5% O₂ in N₂ is added at 90 L/min while maintaining thetemperature between 150°-200° C. The final O₂ /Na ratio is 0.18/1.

EXAMPLE C Invention--Oxidation--Stir Metallic

This example describes another method of catalyst preparation. First,alumina (30 g), prepared by heating a large crystallite pseudoboehmiteto give a surface area of 167 m² /g and a 1.2 wt % loss on ignition at1150° C. is dried in a nitrogen flow at 400° C. for 1 hour and thencooled to room temperature under nitrogen. Then, small pieces ofmetallic sodium (4.5 g) and alumina are placed in a 300 ml roundbottomed flask equipped with a mechanically driven stir paddle. Themixture is heated under nitrogen to 150° C., and at the point metallicsodium starts to melt, stirring is started. The mixture is stirred for2.5 hours, and then cooled to room temperature. Then, 5% O₂ in N₂ isadded at 126 ml/min until the ratio of O₂ /Na is 0.15/1.

EXAMPLE D Comparative--Outside Range--No Oxygen

This example describes another method of catalyst preparation. First,alumina (20.5 g), a large crystallite pseudoboehmite with a surface areaof 250 m² /g and a 2.7 wt % loss on ignition at 150° C., is dried in anitrogen flow at 400° C. for 1 hour, and cooled to room temperatureunder nitrogen. Then pieces of metallic sodium (1.7 g) and alumina areplaced in a 300 ml round bottomed flask equipped with a mechanicallydriven stir paddle. The mixture is heated under nitrogen to 150° C., andat the point metallic sodium starts to melt, stirring is started. Themixture is stirred for 2.5 hours and then cooled to room temperature.

EXAMPLE E Comparative--Outside Range--Oxidation

This example describes a method of catalyst preparation where alumina(17 g), prepared by heating large crystallite pseudoboehmite to give asurface area of 200 m² /g is dried in a nitrogen flow at 400° C. for 1hour and then cooled to room temperature under nitrogen. Then, smallpieces of metallic sodium (2.5 g) and alumina are placed in a 300 mlround bottomed flask equipped with a mechanically driven stir paddle.The mixture is heated under nitrogen to 150° C., and at the pointmetallic sodium starts to melt, stirring is started. The mixture isstirred for 30 min., and then heated to 300° C. for one hour. Themixture is then cooled to room temperature, and 5% O₂ in N₂ is added at126 ml/min until the ratio of O₂ /Na is 0.2/1.

EXAMPLE F Comparative--Outside Range--Oxidation

This example describes a method of catalyst preparation where alumina(30 g), prepared by heating a large crystallite pseudoboehmite to give asurface area of 230 m² /g is dried in a nitrogen flow at 400° C. for 1hour and then cooled to room temperature under nitrogen. Then, smallpieces of metallic sodium (4.5 g) and alumina are placed in a 300 mlround bottomed flask equipped with a mechanically driven stir paddle.The mixture is heated under nitrogen to 150° C., and at the pointmetallic sodium starts to melt, stirring is started. The mixture isstirred for 150 min at 150° C. The mixture is treated with 5% O₂ in N₂is added at 126 ml/min until the ratio of O₂ /Na is 0.15/1.

EXAMPLE G Invention--Inside Range--Starting Material

This example describes one method of catalyst preparation. First,alumina (30 g) with a surface area of 250 m² /g, prepared by heating ofa small crystallite pseudoboehmite alumina, is dried in a nitrogen flowat 400° C. for 1 hour and then cooled to room temperature undernitrogen. Then, small pieces of metallic sodium (4.5 g) and alumina areplaced in a 300 ml round bottomed flask equipped with a mechanicallydriven stir paddle. The mixture is heated under nitrogen to 150° C., andat the point metallic sodium starts to melt, stirring is started. Themixture is stirred for 30 minutes in order to disperse the sodium ontothe alumina. The mixture is then heat soaked at 150° C. for 2 hours withstirring. The mixture was then treated with 5% O₂ in N₂ at a 0.126 1/minrate until the O₂ /Na ratio is 0.2/1.

EXAMPLE H Comparative--Outside Range--Starting Material

This example describes a catalyst prepared according to Example G exceptthat the alumina has a 200 m² /g surface area and is prepared by heatingof a small crystallite pseudoboehmite alumina.

EXAMPLE I Comparative--Outside Range--Starting Material

This example describes a catalyst prepared according to Example G exceptthat the alumina has a 150 m² /g surface area and is prepared by heatingof a small crystallite pseudoboehmite alumina.

EXAMPLE J Comparative--Outside Range--Starting Material

This example describes a catalyst according to Example G except that thealumina has a 156 m² /g surface area and is prepared by heating of agibbsite alumina.

EXAMPLE V-1

Table 5.1 shows results when catalysts (0.25 g) from Examples A-C, and Ewere reacted with high purity VNB (25 g) containing 70 wppmtetrahydroindene (THI) as major impurity at room temperature for 1 hour.All of these catalysts were on an alumina prepared from a largecrystalline pseudoboehmite.

                  TABLE 5.1                                                       ______________________________________                                        Experiments                                                                            Catalyst  Example    Conversion VNB to                               Number   Example   Type       ENB (%)                                         ______________________________________                                        1        A         Comparative                                                                              55                                              2        B         Invention  99.6                                            3        C         Invention  99.6                                            4        E         Comparative                                                                              20                                              ______________________________________                                    

Experiments 2 and 3 illustrate that the activity of catalyst prepared bythe method of this invention is not hindered by the presence of the THIimpurity.

EXAMPLE V-2

Table 5.2 shows results from a series of experiments where VNBcontaining cyclopentadiene (CPD) impurity was isomerized to ENB withcatalysts prepared in Examples A-C, and E. With catalysts A-C, CPD wascompletely removed from the reaction mixture by action of the catalystto give high purity ENB. With catalyst E, about 10 wppm CPD remained inthe reaction product.

Experiments 5-7 show the poisoning effect of CPD on the catalyst sincethe amount of catalyst must be increased to maintain constant conversionas the CPD concentration is increased. A comparison of Experiments 2 and5 show that the invention catalyst is unaffected by 100 wppm CPD.However, catalyst A without oxygen activation is affected by as littleas 20 wppm CPD (compare experiments 1 and 9). Catalyst E prepared withan alumina outside the surface area range of the preferred embodiment,is ineffective as a catalyst when the VNB contains 80 wppm CPD.

                  TABLE 5.2                                                       ______________________________________                                                                 Catalyst                                                                             Starting                                                                            Conversion                              Exp.  Catalyst Example   Loading                                                                              CPD   VNB to                                  Number                                                                              Example  Type      (wt %) (wppm)                                                                              ENB (%)                                 ______________________________________                                        5     B        Invention 1.0    100   99.5                                    6     B        Invention 1.2    210   99.5                                    7     B        Invention 1.5    280   99.5                                    8     C        Invention 1.0    20    99.6                                    9     A        Comparative                                                                             1.0    20    45                                      10    E        Comparative                                                                             1.0    80    0                                       ______________________________________                                    

EXAMPLE V-3

Table 5.3 shows results from a series of experiments where VNBcontaining 4, 7, 8, 9-tetrahydroindene (THI) impurity was isomerized toENB with catalysts prepared in Examples A and B at room temperature. Ineach case, the THI was converted to a mixture of indan, other THIisomers, and indene (which is removed by the catalyst) to give highpurity ENB. THI did not act as a catalyst poison except at high levelsas shown in Experiments 13 and 14. The THI is converted by the catalystand some is removed by the catalyst to give higher purity ENB product. Acomparison of catalysts A and B in experiments 1, 2, 13, and 14 showthat the preferred catalyst is more resistant to poisoning at high THIlevels than catalyst that is not activated with oxygen.

                                      TABLE 5.3                                   __________________________________________________________________________                                Isomenzed                                                       Catalyst                                                                          Starting                                                                          Conversion                                                                          THI  Indan                                        Exp.                                                                             Catalyst                                                                           Example                                                                             Loading                                                                           THI VNB to                                                                              formed                                                                             Formed                                       No.                                                                              Example                                                                            Type  (wt %)                                                                            (wppm)                                                                            ENB (%)                                                                             (wppm)                                                                             (wppm)                                       __________________________________________________________________________     2 B    Invention                                                                           1.0  70 99.6  18    38                                           1 A    Comparative                                                                         4.1  70 99.6  18    38                                          11 B    Invention                                                                           0.9  220                                                                              99.5  58   118                                          12 B    Invention                                                                           0.9  350                                                                              99.5  100  200                                          13 B    Invention                                                                           1.5 2320                                                                              98    280  1080                                         14 A    Comparative                                                                         4.1 2320                                                                              74    60   870                                          __________________________________________________________________________

EXAMPLE V-4

Table 5.4 shows results from a series of experiments where VNBcontaining 1,5-cyclooctadiene (COD) impurity was isomerized to ENB withcatalysts prepared in Examples A and B at room temperature. In eachcase, the COD was quantitatively converted to 1,3-cyclooctadiene to givehigh purity ENB. COD did not act as a catalyst poison except at the highlevels shown in experiments 18 and 19. When corrected for the differentamounts of catalyst, the effect of high COD levels on catalyst A wasgreater than for the preferred catalyst B.

                  TABLE 5.4                                                       ______________________________________                                                                   Catalyst                                                                            Starting                                                                            Conversion                             Experiment                                                                            Catalyst Example   Loading                                                                             COD   VNB to                                 Number  Example  Type      (wt %)                                                                              (wppm)                                                                              ENB (%)                                ______________________________________                                        15      B        Invention 1.0   20    99.6                                   16      A        Comparative                                                                             2.0   20    97                                     17      B        Invention 1.0   800   99.6                                   18      A        Comparative                                                                             2.0   2970  91                                     19      B        Invention 1.0   2970  91                                     ______________________________________                                    

EXAMPLE V-5

Table 5.5 shows results from a series of experiments where VNBcontaining vinylacteylene/CPD adducts (VNBD) impurity was isomerized toENB with catalysts prepared in Examples A-D, F and G. The VNB alsocontained as impurities 600 wppm THI, 100 wppm COD, 5 wppm 0 asVNB-hydroperoxide. Hydroperoxides are catalyst poisons because of theacidity of the --O₂ H function, and the effect on catalyst at the levelin this feed would be equivalent to the poisoning effect of 160 wppmCPD. The COD and THI impurities will not act as catalyst poisons atthese levels in the VNB.

VNBD is a mixture of 5-vinyl-2,5-norbornadiene and5-ethynyl-2-norbornene that is formed in the reaction of vinylacetyleneimpurity with butadiene during VNB synthesis. In each case, the VNBD wascompletely removed from the reaction mixture by action of the catalystto give high purity ENB. The experiments clearly show that the preferredcatalysts B, C, and G have higher poison resistance.

                  TABLE 5.5                                                       ______________________________________                                                                   Catalyst                                                                            Starting                                                                            Conversion                             Experiment                                                                            Catalyst Example   Loading                                                                             VNBD  VNB to                                 Number  Example  Type      (wt %)                                                                              (wppm)                                                                              ENB (%)                                ______________________________________                                        20      B        Invention 1.4   700   99.6                                   21      D        Comparative                                                                             1.0   700   60                                     22      A        Invention 1.4   700   66                                     23      C        Invention 1.4   700   96                                     24      F        Comparative                                                                             1.4   700   60                                     25      G        Invention 1.0   700   99.6                                   ______________________________________                                    

EXAMPLE V-6

This example shows the effect of alumina surface area on catalystactivity when the starting alumina is prepared from a small crystallitepseudoboehmite alumina when using the high purity VNB from Example I.

                  TABLE 5.6                                                       ______________________________________                                        Experiment                                                                            Catalyst Example    Surface Area                                      Number  Example  Type       (m.sup.2 /g)                                                                          Activity No.                              ______________________________________                                        26      G        Invention  250     550                                       27      H        Comparative                                                                              200     250                                       28      I        Comparative                                                                              150     120                                       ______________________________________                                    

EXAMPLE V-7

This example shows the effect of alumina surface area on catalystactivity when the starting alumina is prepared from a large crystallitepseudoboehmite alumina compared to the activity of a catalyst when thealumina support is prepared by heating of a gibbsite alumina. Acomparison of this data with the data in the table below show that highactivity catalyst can not be prepared from gibbsite alumina in anysurface area range. Note that these results were much better than thosein FIG. 1 due to the more optimum oxidation and heat treatingconditions.

                  TABLE 5.7                                                       ______________________________________                                                                           Surface                                    Experiment                                                                            Catalyst Example   Alumina Area  Activity                             Number  Example  Type      Precursor                                                                             (M.sup.2 /G)                                                                        Number                               ______________________________________                                        28      C        Invention Large   167   550                                                             Pseudoboeh                                                                    mite                                               29      J        Comparative                                                                             Gibbsite                                                                              158   130                                  ______________________________________                                    

EXAMPLE V-8

This example shows the isomerization of VNB to give high quality ENB inthe presence of greater than 0.5 wt. % vinylcyclohexene (VCH). Thevinylcyclohexene is converted to ethylbenene which is an inert diluentin the process to prepare EPDM rubber from the ENB. This isomerizationreaction is run under negative pressure or swept with nitrogen to removehydrogen evolved during conversion of the VCH to ethylbenzene.

A mixture containing 70 wt. % VNB and 30 wt % VCH is mixed with 2.7 wt.% catalyst of Example C at 70° C. After 2 hours, the mixture wasanalyzed by gas chromatography. The conversion of VNB to ENB was 99.5%and the conversion of VCH to ethylbenzene was 99.9%. This is a suitablefeed to an EPDM manufacturing plant.

The examples set forth above illustrate aspects of the invention and arenot limitations on the scope of the invention which is set forth in theclaims below. Many other variations and modifications may be made to theprocess and catalyst described above without departing from the conceptof the present invention. Accordingly, it should be clearly understoodthat the methods referred to in the foregoing description areillustrative only and are not intended as limitations on the scope ofthe invention.

We claim:
 1. An activated isomerization catalyst prepared by:providing asubstantially dry support material consisting essentially of an aluminaprepared from a starting material consisting essentially of apseudoboehmite wherein said alumina has a surface area selected from thegroup consisting of in the range of from about 125 m² /g to about 195 m²/g when prepared from a starting material consisting of a firstpseudoboehmite having an average crystallite size substantially the sameas to a catapal grade pseudoboehmite or wherein said alumina has asurface area in the range of from about 220 m² /g to about 280 m² /gwhen prepared from a starting material of a second pseudoboehmite havingan average a crystallite size smaller than a catapal gradepseudoboehmite; mixing a metallic form alkali metal and thesubstantially dry support material under conditions comprising a timeand an elevated temperature effective to ensure substantially completethermal mixing and to produce a catalyst precursor mixture comprising asubstantially uniform dispersion of the alkali metal on the support;activating the catalyst precursor mixture by treatment with anoxygen-containing gas under conditions effective to produce an activatedcatalyst which maintains a higher rate of activity during isomerizationthan said catalyst maintains in the absence of said treatment with saidoxygen-containing gas.
 2. An activated isomerization catalyst preparedby:providing a substantially dry support material consisting essentiallyof an alumina prepared from a starting material consisting essentiallyof a pseudoboehmite wherein said alumina has a surface area selectedfrom the group consisting of in the range of from about 125 m² /g toabout 195 m² /g when prepared from a starting material consisting of afirst pseudoboehmite having an average crystallite size substantiallythe same as a catapal grade pseudoboehmite or wherein said alumina has asurface area in the range of from about 230 m² /g to about 260 m² /gwhen prepared from a starting material of a second pseudoboehmite havingan average a crystallite size smaller than a catapal gradepseudoboehmite; mixing a metallic form of an alkali metal and thesubstantially dry support material under conditions comprising a timeand an elevated temperature effective to ensure substantially completethermal mixing and to produce a catalyst precursor mixture comprising asubstantially uniform dispersion of the alkali metal on the support;activating the catalyst precursor mixture by treatment with anoxygen-containing gas under conditions effective to produce an activatedcatalyst which maintains a higher rate of activity during isomerizationthan said catalyst maintains in the absence of said treatment with saidoxygen-containing gas.
 3. An activated isomerization catalyst inaccordance with claim 1, wherein said alumina has a surface area of 140to 180 m² /g when prepared from a starting material consisting of asecond crystallite pseudoboehmite.
 4. An activated isomerizationcatalyst in accordance with claim 1, wherein said alkali metal isselected from the group consisting of lithium, sodium, potassium,cesium, rubidium, and mixtures thereof.
 5. An activated isomerizationcatalyst in accordance with claim 4, wherein the alkali metal is sodium.6. An activated isomerization catalyst in accordance with claim 5,wherein the temperature at which the sodium is dispersed on the drysupport material in step (b) is from about 100° C. to 300° C.
 7. Anactivated isomerization catalyst in accordance with claim 1, wherein thecontact between said catalyst precursor mixture and saidoxygen-containing gas in step (d) occurs at a temperature of 100° C. to250° C.
 8. An activated isomerization catalyst in accordance with claim7, wherein the ratio of total moles of activating oxygen to total atomsof alkali metal in step (d) is in the range of 0.005:1 to 1:1.
 9. Anactivated isomerization catalyst in accordance with claim 8, wherein theratio of total moles of activating oxygen to total atoms of alkali metalin step (d) is in the range of 0.05:1 to 0.2:1.
 10. An activatedisomerization catalyst in accordance with claim 7, wherein saidoxygen-containing gas comprises nitrogen and from about 2 to 10 molepercent oxygen.
 11. An activated isomerization catalyst in accordancewith claim 1, wherein the activity number is greater than
 50. 12. Anactivated isomerization catalyst in accordance with claim 11, whereinthe activity number is greater than
 100. 13. An activated isomerizationcatalyst in accordance with claim 12, wherein the activity number isgreater than
 150. 14. A process for preparing a high quality olefincomprising catalytically isomerizing a stream comprising an olefin whichcomprises contacting the stream comprising an olefin with an activatedcatalyst, wherein the activated catalyst is prepared in accordance withclaim
 1. 15. A process in accordance with claim 14, wherein the streamcomprising an olefin further comprises one or more reactive impurities.16. A process in accordance with claim 15, wherein said reactiveimpurities are selected from the group consisting of other mono olefins,acidic oxygenates, and diene impurities.
 17. A process in accordancewith claim 16, wherein said diene impurities are selected from the groupconsisting of cyclopentadiene, cyclooctadiene, tetraahydroindene,vinylnorbornadiene, ethynyinorborene, hydroperoxides, vinylcyclohexenes,and methyl vinylcyclohexenes.
 18. A process in accordance with claim 14,wherein said olefin is alkenyl bridged compound.
 19. A process inaccordance with claim 18, wherein said alkenyl bridged ring compound is5-vinyl-2-norbornene.
 20. A process in accordance with claim 19, whereinsaid olefin is 5-vinyl-2-norbornene.
 21. A process in accordance withclaim 14, wherein the contact between the stream comprising an olefinand the activated catalyst occurs at a temperature from about 20° toabout 100° C.
 22. The catalyst of claim 1 wherein said alumina has asurface area in the range of from about 140 m² /g to about 180 m² /gwhen prepared from a starting material of a said first pseudoboehmite.23. The catalyst of claim 1 wherein said alumina has a surface area inthe range of from about 150 m² /g to about 180 m² /g when prepared froma starting material of a said first pseudoboehmite.
 24. The catalyst ofclaim 1 wherein said alumina has a surface area in the range of fromabout 230 m² /g to about 270 m² /g when prepared from a startingmaterial of a said second pseudoboehmite.
 25. The catalyst of claim 1wherein said alumina has a surface area of about 250 m² /g when preparedfrom a starting material of a said second pseudoboehmite.
 26. Anactivated isomerization catalyst prepared by:providing a substantiallydry support material consisting essentially of an alumina prepared froma starting material consisting essentially of a pseudoboehmite whereinsaid alumina has a surface area selected from the group consisting of inthe range of from about 125 m² /g to about 195 m² /g when prepared froma starting material consisting of a first pseudoboehmite having anaverage crystallite size substantially the same as a catapal gradepseudoboehmite or wherein said alumina has a surface area in the rangeof from about 220 m² /g to about 280 m² /g when prepared from a startingmaterial of a second pseudoboehmite having an average a crystallite sizesmaller than a catapal grade pseudoboehmite; mixing a metallic form ofan alkali metal comprising sodium and the substantially dry supportmaterial under conditions comprising a time and an elevated temperatureeffective to ensure substantially complete thermal mixing and to producea catalyst precursor mixture comprising a substantially uniformdispersion of the alkali metal on the support; activating the catalystprecursor mixture by treatment with an oxygen-containing gas underconditions effective to produce an activated catalyst which maintains ahigher rate of activity during isomerization than said catalystmaintains in the absence of said treatment with said oxygen-containinggas.